Preparation method for Pb[(Znx Mg1-x)1/3 Nb2/3 ]O3

ABSTRACT

A preparation method for Pb[(Zn x  Mg x-1 ) 1/2  Nb 2/3  ]O 3  ceramic, wherein 1&lt;x=0.25, without the use of stabilizers such as SrTiO 3 , PbTiO 3 , BaTiO 3 , or PbZrO 3 . The method comprises the steps of: 
     (a) mixing about 14.0 wt % of MgO with 86.0 wt % of Nb 2  O 5 , 
     (b) calcining the mixture in step (a) at a temperature about 1000° C. for 4 hours, 
     (c) reacting about 68.6 wt % PbO with the calcined product obtained in step (b), and 
     (d) mixing about 10.2-49.8 wt % PbO, about 1.2-6.0 wt % ZnO, and about 4.0-19.8 wt % Nb 2  O 5  with product of about 84.4-24.2 wt % PMN and carrying out the steps of grinding, drying and calcining at temperatures 850° C. to 950° C. for about 4 hours, 
     (e) sintering at temperatures of from 950° C.-1200° C. for 2 hours.

BACKGROUND OF THE INVENTION

Pb(Zn_(1/3) Nb_(2/3))O₃ (abbreviated as PZN) ceramic and Pb(Mg_(1/3)Nb_(2/3))O₃ (abbreviated as PMN) ceramic are regarded as important rawmaterials in making of ceramic drivers and integrated layered capacitorsmainly due to their high coefficients of electrostrictive and dielectricconstants. However, only when PZN and PMN possess the structure ofperovskite, then both of them possess the above properties andusefulness. Moreover, in the process of making these ceramics, it isvery often that pyrochlore phase will occur which deteriorates theseproperties. Recently, the synthesis of PMN ceramic can be obtained byfirst pre-synthesizing the MgNb₂ O₆ phase and then reacting with PbO inorder to form perovskite phase of PMN. While in the synthesis of PZNceramic, even the ZnNb₂ O₆ phase is formed first, the perovskite phasecannot be fully obtained. As a result, common stabilizers such asSrTiO₃, PbTiO₃, BaTiO₃, Ba(Zn_(1/3) Nb_(2/3))O₃ or PbZrO₃, etc. have tobe added to facilitate the formation of PZN perovskite. The aboveadditives can be used to stabilize the PZN perovskite but they may causeunfavorable influence on the inherent excellent properties of PZN. Inlight of the fact that the PMN perovskite ceramic possesses theproperties similar to the PZN, it is advisable to synthesize the stablePMN perovskite first and then stabilize the PZN perovskite phase ceramicby employing the synthesized PMN as the additive, and form the Pb(Zn_(x)Mg_(1-x))_(1/3) Nb_(2/3) ]O₃ perovskite phase ceramic raw materials.According to the preparation method of the present invention, noaddition of additive as stabilizer is needed to effect the process. Inconventional method of ceramics preparation with PZN as the basis,components such as PbO, ZnO, and Nb₂ O₅ are mixed together without theaddition of perovskite phase stabilizer (such as SrTiO₃, PbTiO₃,BaTiO₃), as a result, the perovskite phase PZN as indicated in FIG. 1cannot be obtained. Consequently, the addition of a stabilizer isnecessary. Furthermore, in the process of making the desired productwith an appropriate ratio of PbO, ZnO, MgO and Nb₂ O₅, the amount of MgOshould be greater than 35 mole %. By this process, about 80% ofperovskite phase can be obtained. The properties of the obtained producthas been illustrated in FIG. 4. It seems that the coefficient ofdielectric constant does not exceed 13000.

Japanese Patent 57-25607 discloses a dielectric ceramic compositionconsisting 68.03-69.07wt % Pb₃ O₄, 2.43 to 3.98 wt % MgO, 0.15 to 3.15wt % ZnO and 26.37 to 26.78 wt % Nb₂ O₅. Pb₃ O₄, MgO and Nb₂ O₅ aremixed and sintered at 850° C. to produce Pb(Mg_(1/3) Nb_(2/3))O₃.Powered Pb₃ O₄, ZnO and Nb₂ O₅ were mixed and sintered at 850° C. toproduce Pb(Zn_(1/3) Nb_(2/3))O₃. 75 parts wt of Pb(Mg_(1/3) Nb_(2/3))O₃,25 part wt. of Pb(Zn_(1/3) Nd_(2/3))O₃ and a vinyl acetate binder aremixed and compacted, and sintered at 1050° C. for 1 hr. The sinteredproduct has a dielectric constant of 14000 at 25° C.

SUMMARY OF THE INVENTION

Therefore, it is the object of the present invention to provide apreparation method in producing stable Pb[(Zn_(x) Mg_(1-x))_(1/3)Nb_(2/3) ]O₃ ceramic by first synthesizing a stable PMN ceramicperovskite phase and then making use of this produced material as astabilizer for the perovskite phase of the Pb(Zn_(1/3) Nb_(2/3))O₃, andfinally a Pb[(Zn_(x) Mg_(1-x))_(1/3) Nb_(2/3) ]O₃ ceramic havingperovskite phase is thus obtained. The produced ceramic possessesexcellent properties in industrial application.

It is another object of the present invention to provide a preparationmethod in producing a stable Pb[(Zn_(x) Mg_(1-x))_(1/3) Nb_(2/3) ])₃ceramic without the addition of a further stabilizer such as SrTiO₃,BaTiO₃, etc..

It is a further object of the present invention to provide a preparationmethod in producing a stable Pb[(Zn_(x) Mg_(1-x))_(1/3) Nb_(2/3) ]O₃ceramic, wherein the obtained ceramic is non-degradable and possesseshigh coefficient of electrostrictive friction and dielectric constant.

These and other objects will become readily apparent from the detaileddescription which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 illustrates the X-ray diagram of the PbO--ZnO--Nb₂ O₅ ceramicwithout the addition of perovskite phase stabilizer in a conventionalmethod.

FIG. 2 illustrates the X-ray diagram of the PbO--ZnO--Nb₂ O₅ ceramicswith the addition of 0.12 mol % SrTiO₃ in a conventional method.

FIG. 3 illustrates the dielectric features of the product in accordancewith FIG. 2.

FIG. 4 illustrates the dielectric features of a sintered ceramics in aconventional method without the addition of SrTiO₃ whereas PbO, ZnO, MgOand Nb₂ O₅ being mixed with an appropriate ratio, wherein the peak valueof the dielectric coefficient is maximum at 13000.

FIG. 5 illustrates the perovskite phase contents for the ceramicsaccording to the present invention in comparison with the conventionalmethod.

FIG. 6 illustrates the effect of ZnO on the Es (Dielectric Constant) andTc of PZMN in accordance with the present invention.

FIG. 7 illustrates the relationship between the dielectric constant andthe amount of a ZnO in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a preparation method of Pb[(Mg_(1-x)Nb_(x))_(1/3) ]O₃ ceramic materials with stable perovskite structure byutilizing a stable PMN ceramic as the stabilizer.

In this process, about 13.736 wt % of MgO and about 86.264 wt % of Nb₂O₅ are mixed, ground and calcined to form MgNb₂ O₆. The calciningprocess is carried out at 1000° C. for approximately 4 hours to produceMgNb₂ O₆. PbO is added to the above MgNb₂ O₆ and the grinding andcalcining steps are repeated. It is calcined at 900° C. for 4 hours toobtain the perovskite phase of Pb(Mg_(1/3) Nb_(2/3))O₃. PbO, ZnO, andNb₂ O₅ are then mixed and ground with the obtained Pb(Mg_(1/3)Nb_(2/3))O₃ ground. Having the above product dried and then calcined attemperature range from 850° C. to 950° C. for 4 hours. The obtainedproduct is again ground and sintered at temperatures of 950° C. to 1200°C. for another 2 hours. The final product obtained is Pb--Mg--Zn--Nb₂ O₅ceramic.

Referring to FIG. 5 which illustrates the perovskite phase contents forthe ceramics according to the present invention in comparison with theconventional method. In the figure, curve PMN--P--Z--N indicates thatwhen the amount of PMN ceramic added is greater than 25 mol %, aPb[(Zn_(x), Mg_(1-x))_(1/3) Nb_(2/3) ]O₃, where x is in the range from 0to 0.75, ceramic material with almost 100% perovskite is obtained. 0nthe other hand, in traditional P-Z-M-N curve, only when the amount ofMgO exceeds 35 mol %, the obtained product Pb[Zn_(y), Mg_(1-y))_(1/3)Nb_(2/3) ]O₃, y is between 0 and 0.65, possesses about 85% perovskiteand no matter how much the amount of MgO is increased, to obtain a 100%perovskite is not possible. Thus, it is apparent that the preparationmethod in accordance with the present invention exceeds the extremelimitation of the traditional 85% perovskite phase and attains thehighest efficacy of 100% perovskite. Moreover, merely 25% of the PMN isused which is comparatively less than that in the conventional method.

Referring to FIG. 6, which illustrates the effect of ZnO on the Es andTc of PZMN in accordance with the present invention. The dielectricconstant is varied with respect to x of Pb[(Zn_(x) Mg_(1-x))_(1/3)Nb_(2/3) ]O₃, wherein when x is equal to 0.65 (which has been denoted byΔ), the dielectric constant attains a maximum of 22×10³. Referring toFIG. 7, which illustrates the relationship between the dielectricconstant and the amount of ZnO in accordance with the present invention.In the figure, curve PMN--P--Z--N indicates that the dielectric constantis at a maximum of 22×10³, which is a lot higher than that of theconventional P--Z--M--N of 12× 10³. Obviously, this further indicatesthe advantages and efficacies of the ceramic in accordance with thepresent invention.

The following example is offered by way of illustration. The example isnot intended to be limiting to the scope of the invention in any respectand should not be so construed.

EXAMPLE Example 1

13.736wt. % of MgO and 86.264 wt % of Nb₂ O₅ were mixed ground andcalcined at 1000° C. for 4 hours to form MgNb₂ O₆ and 68.625 wt % of PbOwas added to the above obtained product to form PMN perovskite phase ofPb(Mg_(1/3) Nb_(2/3))O₃. By making use of the PMN perovskite phase as astabilizer, 43.419 wt. % of PbO, 5.2765 wt. % of ZnO, 17.2368 wt % ofNb₂ O₅ and 34.0677 wt % of PMN were ground and mixed together in spirit.The product was dried at room temperature and calcined again at atemperature in the range of 850° C. to 950° C. for approximate 4 hours.Repeat the steps of grinding, and sintering the above obtained productat a temperature in the range of 950° C. to 1200° C. for about 2 hours.The final product according to this process is a Pb(Zn₀.65 Mg₀.35)_(1/3)Nb_(2/3) O₃ ceramic material with almost 100% perovskite.

From the foregoing it will be appreciated that, although specificembodiment of the invention has been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notintended to be limited except as by the appended claims.

We claim:
 1. A preparation method for Pb[(Zn_(x) Mg_(1-x))_(1/3)Nb_(2/3) ]O₃ ceramics comprising the steps of:(a) mixing about 14.0 wt %of MgO with 86.0 wt % of Nb₂ O₅, (b) grinding and calcining the mixtureobtained in step (a) at a temperature about 1000° C. for 4 hour, (c)reacting about 68.6 wt % PbO with the calcined product obtained in step(b), and then grinding and calcining at 900° C. 40h to from PMN[(Pb(Mg_(1/3) Nb_(2/3))O₃ ], (d) mixing about 10.2-49.8 wt % PbO,1.2-6.0 wt % ZnO, and about 4.0-19.8 wt % Nb₂ O₅ with about 84.4-24.2 wt% PMN [(PB(Mg_(1/3) Nb_(2/3))O₃ ] obtained in (c) carrying out the stepsof grinding, drying and calcining at temperatures of 800° C. to 1200° C.for 4h, then sintering at temperatures of from 950°-1200° C. for 2hr,thereby Pb[(Zn_(1-x) Mg_(x))_(1/3) Nb_(2/3) ]O₃ ceramic having almost100% of perovskite phase is obtained.
 2. A method of claim 1 forpreparing a Pb[Zn_(x) Mg_(1-x))_(1/3) Nb_(2/3))O₃ ceramic, wherein thevalue of x is up to 0.75.
 3. A preparation method for Pb[(Zn_(x)Mg_(1-x))_(1/3) Nb_(2/3) ]O₃ ceramic, wherein the calcining temperaturesare about 800° C. to 1200° C.
 4. A product produced according to themethod of claim 1 having a dielectric constant greater than about15,000.
 5. A product produced according to the method of claim 2 havinga dielectric constant greater than about 15,000.
 6. A product producedaccording to the method of claim 3 having a dielectric constant greaterthan about 15,000.